This invention relates to a system for integrally controlling an automatic transmission and an engine.
Automatic transmissions for vehicles, having gear shift mechanisms, a plurality of frictionally engaging devices, and hydraulic control devices operated to selectively switch the engagements of the frictionally engaging devices, so that any one of a plurality of gear stages can be achieved are well known in the transmission art.
In the automatic transmission as described above, to reduce the shift shocks thereof, an accumulator is provided in oil lines leading to the frictionally engaging devices.
When pressure is fed anew, this accumulator forms a so-called oil pool in the oil line, so that a region where oil pressure acting on the frictionally engaging devices does not rise sharply, can be created.
In general, in order to decrease a rate of change with time of an output shaft torque as much as possible, it is preferable to constantly or gradually decrease supplied oil pressure when the frictionally engaging devices are engaged. For example, in the case where the frictionally engaging devices are clutches, since rotation is started simultaneously with the start of engagements, centrifugal oil pressure is generated. Since this centrifugal oil pressure is applied to the actually supplied oil pressure, it is preferable that the supplied oil pressure itself be gradually decreased, accordingly.
However, the oil pressure characteristics obtained by the conventional accumulator present such a problem that the freedom of design is very small due to the construction of the accumulator. In oil pressure control using an accumulator, for example, along with the movement of an accumulator piston, oil pressure cannot help but be increased by a value of the increased load of a spring attached to the aforesaid accumulator piston. When this rate of increase is to be lowered as much as possible, a spring constant of a spring attached to the accumulator piston is lowered in general. However, there are many cases where the spring constant cannot be desirably lowered due to restrictions including loads needed at the beginning and end of movement of this accumulator piston, the size of the accumulator, the quality of the spring material and the like.
Further, since the accumulator forms the so-called oil pool to hold oil pressure constant, the accumulator needs a considerable volume itself, in general. Thus it is an obstacle to reduce the automatic transmission in size.
To obviate the above-described disadvantages of the prior art, the applicant has provided, in Japanese patent application Ser. No. 287383/85 (not laid open yet), a shift control device of an automatic transmission in a vehicle, wherein, the accumulator is more compact in size, and moreover, shift shocks are reduced further, so that improved shift smoothness can be obtained. Therein is provided a device capable of desirably controlling a rate of change with time of oil pressure supplied to the frictionally engaging devices, wherein a predetermined time during shifting is detected, and the rate of change with time of the oil pressure supplied to the frictionally engaging devices is changed and controlled from this predetermined time. As a result, an oil pressure operating upon the frictionally engaging devices during shifting (this oil pressure being commensurate to the torque transmitting force in the frictionally engaging devices) can be controlled to minimize the shift shocks.